GSEA revealed changes of sphingolipid metabolism in the liver of 5-month-old GIPRdn transgenic pigs. A: Enrichment plot showing the distribution of genes of the KEGG pathway sphingolipid metabolism (vertical bars) in the list of genes expressed in liver samples ranked according to their differential expression between GIPRdn transgenic and control pigs. The enrichment profile (green curve) shows a nonrandom distribution indicated by a roughly triangular outline and a peak close to one of the extremes of the signal-to-noise ordered dataset. This distribution means that a higher proportion of the pathway genes than expected under the null hypothesis are upregulated in GIPRdn transgenic animals and fewer than expected are downregulated or neutral. The leading edge subset containing the most upregulated genes are the genes positioned left of the peak in the enrichment curve profile. These genes are listed in and highlighted (red frame) in panel B. B: Partial sphingolipid metabolism pathway highlighting the products of genes that were upregulated in GIPRdn transgenic pigs compared with controls and their enzymatic functions. The enzymes encoded by ASAH2 and UGT8, which were the most upregulated genes of this pathway in GIPRdn transgenic pigs, directly decrease the availability of ceramide, which is required for SM biosynthesis. Thus, the findings of the liver transcriptome analysis are in line with reduced plasma SM levels of 5-month-old GIPRdn transgenic pigs. ACER3, alkaline ceramidase 3 (EC:3.5.1.23); ASAH2, N-acylsphingosine amidohydrolase (nonlysosomal ceramidase) 2 (EC:3.5.1.23); CERS1–6, ceramide synthase 1–6 (EC:2.3.1.24); DEGS2, sphingolipid delta-4 desaturase (EC:1.14.-.-); GALC, galactosylceramidase (EC:3.2.1.46); SGMS1/2, SM synthase 1/2 (EC:2.7.8.27); SGPL1, sphingosine-1-phosphate lyase 1 (EC:4.1.2.27); SGPP2, sphingosine-1-phosphate phosphatase 2 (EC:3.1.3.-); SMPD1–4, SM phosphodiesterase 1–4 (EC:3.1.4.12); SPHK1/2, sphingosine kinase 1/2 (EC:2.7.1.91); UGT8, UDP glycosyltransferase 8 (EC:2.4.1.45); EC 3.1.4.41, SM phosphodiesterase D.